Hydrocratic generator

ABSTRACT

A hydraulic power generation system is provided for generating power using a pseudo-osmosis process which efficiently exploits the osmotic energy potential between two bodies of water having different salinity concentrations. The method and apparatus of the present invention does not require the use of a semi-permeable membrane or other specially formulated material, nor does it require heating or cooling of the fresh water or salt water solution. Moreover, the device may be used to recover energy from a wide variety of fresh water sources, including treated or untreated river run-off, treated waste-water run-off or effluent, storm-drain run-off, partly contaminated fresh water run-off, and a wide variety of other fresh water sources. The device is well suited to power production in a wide variety of geographic locations and under a wide variety of conditions. The invention has particular advantage for use in remote regions where electrical power generation by conventional means may be commercially infeasible or impractical.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 09/415,170 filed Oct. 8, 1999, now U.S. Pat. No. 6,313,545,which is incorporated herein. Ser. No. 09/415,170 itself claims thebenefit of Provisional Patent Applications Nos. 60/123,596 filed on Mar.10, 1999 and 60/141,349, filed on Jun. 28, 1999 both of which areincorporated herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to hydraulic power generation systems and,in particular, to an apparatus and method for generating power using anovel pseudo-osmosis process which efficiently exploits the osmoticenergy potential between two bodies of water having different salinityconcentrations.

2. Description of the Related Art

About 20% of the world's electricity is generated using hydropower. Inthe United States alone this resource accounts for about 12% of thenation's supply of electricity, producing more than 90,000 megawatts ofelectricity annually and meeting the needs of approximately 28.3 millionconsumers each year. Hydropower is a clean source of natural energy. Notonly is it environmentally friendly (and even beneficial in terms offlood control, etc.), but it is also extremely cost-efficient. In theNorthwest, for example, electricity from hydropower plants typicallycosts about $10 per megawatt hour to produce. This compares to about$60, $45 and $25 per megawatt hour to produce electricity at nuclear,coal and natural gas power plants, respectively.

However, current hydroelectric power plants are configured to recoveronly the energy component of water that is released as a result ofelevational changes. In particular, hydroelectric power is typicallygenerated by dropping 200-300 feet-head (61-91 m-head) of fresh waterfrom a higher elevation to a lower elevation across a rotating turbinecoupled to an electrical generator. The exhaust water flow is dischargedat the lower elevation as energy-depleted fresh water run-off. But, aswill be explained in more detail below, this fresh water run-off is notcompletely depleted of energy. In fact, the amount of remainingrecoverable energy in the discharged fresh water can be as great as theequivalent of 950 feet-head (290 m-head) of water or more. To understandthe nature and origin of this additional recoverable energy component itis helpful to look at how fresh water is created.

Fresh water begins as water vapor that is evaporated from the oceans bysolar energy. This water vapor rises into the atmosphere whereupon itcools. Cooling causes the water vapors to condense into clouds,ultimately resulting in precipitation. Some of this precipitation occursover land masses forming fresh-water lakes, accumulated snow-fall and anextensive network of associated rivers, streams, aquifers and otherforms of water run-off. Ultimately, all or virtually all of this freshwater run-off makes its way back to the oceans, thus completing thecycle. In fact, throughout the world enormous quantities of fresh wateris freely washed into the ocean each year as part of the naturallyoccurring water cycle and/or as part of various human interventions suchas hydro-power facilities, municipal waste water treatment facilities,and the like.

The overall driving force behind the water cycle is solar energyradiating from the sun over millions of square miles of exposed oceanwaters each day. It is this solar energy that causes evaporation offresh water vapors from the relatively high-saline ocean waters. Theamount of radiant solar energy absorbed in this process is enormous,representing approximately 2,300 kJ/kg (0.64 kW-hr/kg) of waterevaporated. This absorbed energy causes a concomitant increase in thelatent energy or enthalpy of the evaporated water. The vast majority ofthis latent energy (approximately 99%) is dissipated as heat energy intothe atmosphere upon re-condensing of the water vapors into clouds.However, a small but significant portion of this latent energy(approximately 0.13%) remains stored within the resulting fresh-waterprecipitation. This remaining non-dissipated stored energy representsthe so-called “free energy of mixing” (or “heat of mixing”) of freshwater into sea water. Specifically, it is the additional incrementalenergy (beyond the energy of evaporation of pure water) that is requiredto separate the fresh water (or other solvent) from the salt watersolution (or other solvent/solute solution).

The free energy of mixing reflects an increase in entropy of water (orother solvent) when it is transformed from its pure (fresh-water) stateto its diluted (salt-water) state. It is a physical property ofsolvents, such as water, that they have a natural tendency to migratefrom an area of relatively low solute concentration (lower entropy) toan area of relatively high solute concentration (higher entropy). Thus,an entropy gradient is created whenever two bodies of water or othersolvent having differing solute concentrations are brought into contactwith one another and begin to mix. This entropy gradient can bephysically observed and measured in the well-known phenomena known asosmosis.

Osmosis is the flow of water through a selectively permeable membrane(i.e., permeable to water, but impermeable to dissolved solutes) from alower concentration of solute to a higher one. It is a colligativephenomenon—that is, it is not dependent on the nature of the solute,only on the total molar concentration of all dissolved species. Purewater is defined as having an osmotic potential of zero. All water-basedsolutions have varying degrees of negative osmotic potential. Manyreferences discuss osmotic potential in terms of pressure across asemi-permeable membrane since the easiest way to measure the effect isto apply pressure to the side of the membrane with higher negativeosmotic potential until the net flow is canceled. “Reverse osmosis” isthe phenomena that occurs when additional pressure is applied across aselectively permeable membrane to the point of reversing the naturalflow-direction there-through, resulting in separation of the solventfrom the solute.

But, just as it takes energy to separate an amount of fresh water from abody of salt water, such as through solar evaporation or using thewell-known reverse-osmosis desalinization process, remixing the freshwater back into the ocean waters results in the release of an equalamount of stored energy (approximately 2.84 kJ/kg) of fresh water. Ifthis source of latent stored energy could somehow be efficientlyexploited, it could result in the production of enormous amounts ofinexpensive electrical power from a heretofore untapped and continuallyrenewable energy resource.

For example, if 30% of the average flow from the Columbia River could bediverted into a device that recovered this latent free energy of mixingor osmotic energy potential at 100% efficiency, it would generate 6,300megawatts of power. To put this in perspective, the currenthydroelectric facility of the Grand Coulee Dam on the Columbia River(the largest hydroelectric power plant in the United States and thethird largest in the world) generates a peak output of 6,800 megawatts.See, http://www.cqs.washington.edu/crisp/hydro/gcl.html. If the flowfrom the Weber River into the Great Salt Lake could be diverted throughsuch a device, it would generate 400 megawatts of power. See, e.g.,http://h20.usgs.gov/public/realtime.html for a statistical survey ofother U.S. hydrographic data. Such a device would be of enormous benefitto people throughout the world, particularly those in remote regionswhere electrical power generation by conventional means may be difficultor impractical.

Various proposals have been made over the years for possible ways ofcommercially exploiting this attractive source of natural, renewableenergy. For example, Jellinek (U.S. Pat. No. 3,978,344) proposed to passfresh water through a semi-permeable membrane into a salt or brinesolution. The resulting osmotic pressure differential across themembrane would then be used to eject a stream of salt water through anoutlet orifice to drive a water wheel coupled to an electrical powergenerator to generate electrical power. Similarly, Loeb (U.S. Pat. No.3,906,250) describes a method and apparatus for generating powerutilizing pressure retarded osmosis through a semi-permeable membrane.

Each of the above approaches, like many others heretofore advocated,rely on a forward osmosis process utilizing a semi-permeable membrane toobtain useful work from the difference in osmotic potential exertedacross the membrane. While such systems may have useful application on asmall scale under certain limited conditions, full-scale commercialdevelopment and exploitation of such power-generation systems ishampered by the large membrane surface area required to achieve adequateflow rates and the expense and difficulty of maintaining suchsemi-permeable membranes. Although modern advances in syntheticmaterials have produced membranes that are very efficient at rejectingbrine solutes and are tough enough to withstand high pressures, suchmembranes are still susceptible to clogging, scaling and generaldegradation over time. For example, river water used as a fresh-watersource would likely carry a variety of solutes and other suspendedsediment or contaminants which could easily clog the membrane, requiringfiltering and/or periodic cleaning. Treated effluent from a municipalwaste-water treatment plant used as a fresh water source would presentsimilar and possibly additional complications, making such approachcommercially impractical.

Urry (U.S. Pat. No. 5,255,518) proposed an alternative method andapparatus for exploiting osmotic energy potential in a manner that doesnot utilize a semi-permeable membrane. In particular, Urry proposed theuse of a specially formulated bio-elastomer. The bio-elastomer isselected such that it alternately and reversibly contracts or expandswhen exposed to different concentrations of a brine solution. Amechanical engine is proposed for converting the expansion andcontraction motion of individual bio-elastomer elements into usefulwork. While such a system demonstrates the usefulness of the generalapproach, the proposed system utilizing bio-elastomer elements or thelike is not readily suited for large-scale, low cost energy production.To produce useful energy on a commercial scale such a system wouldrequire a vast number of bio-elastic elements having very large surfacearea. Again, the exposed surface area would be subject to contaminationand degradation over time, as with the membranes discussed above, makingsuch a system prohibitively expensive to construct and maintain.

Assaf (U.S. Pat. No. 4,617,800) proposed another alternative apparatusfor producing energy from concentrated brine in a manner that does notutilize a semi-permeable membrane or specially formulated bio-elastomer.In particular, Assaf proposed using a system of steam evaporation andre-condensation. In this approach steam is first generated by heatingfresh water in an evaporator and passing the steam through a turbine todrive an electric generator. The condensed steam is then passed to acondenser wherein it is contacted with a flow of concentrated brine,generating heat from the heat of dilution of the brine. It is proposedthat the evolved heat would then be transmitted though a heat-exchangerelement back to the evaporator to generate steam from the fresh water.While this approach generally avoids the membrane and large surface areacontamination problems discussed above, it is not ideally suited forlarge-scale, low cost energy production. This is because of the numberand complexity of components involved and the need to heat and cool thefresh water in pressure sealed evaporator and condenser units. Such asystem would be expensive to construct and operate on a commercialscale.

Thus, there remains a need for a method and apparatus for efficientlyexploiting the osmotic energy potential between fresh water and seawater (and/or other solutions).

SUMMARY OF THE INVENTION

Accordingly, it is an aspect to provide an improved apparatus and methodfor generating power using a novel forward osmosis process whichefficiently exploits the osmotic energy potential between two bodies ofwater having different salinity concentrations.

Advantageously, the method and apparatus of the present invention doesnot require the use of a semi-permeable membrane or other speciallyformulated material, nor does it require heating or cooling of the freshwater or salt water solution. Moreover, the present invention mayrecover energy from a wide variety of fresh water sources, includingtreated or untreated river run-off, treated waste-water run-off oreffluent, storm-drain run-off, partly contaminated fresh water run-off,and a wide variety of other fresh water sources. Thus, the presentinvention is well suited to large scale power production in a widevariety of geographic locations and under a wide variety of conditions.The invention has particular advantage for use in remote regions whereelectrical power generation by conventional means may be commerciallyinfeasible or impractical.

In accordance with one embodiment the present invention provides amethod for generating power from the differences in osmotic potentialbetween a source of relatively low salinity water and a source ofrelatively high salinity water. Relatively low salinity water isconducted through a first tube. The relatively low salinity water isthen directly contacted with the relatively high salinity water in anenclosed second tube to form a mixture. The second tube is in fluidcommunication with the source of relatively high salinity water throughone or more openings. The contacting of the two different salinitywaters causes upwelling of the mixture within the second tube. Thismixture is passed through a power generation unit to generate mechanicaland/or electrical power.

In accordance with another embodiment the present invention provides amethod for generating power from the osmotic energy potential of freshwater. A source of relatively low salinity water is conducted to apredetermined depth in a body of relatively high salinity water througha down tube having a first cross-sectional area. The relatively lowsalinity water is directly contacted with the relatively high salinitywater from the predetermined depth in an up tube having a secondcross-sectional area, forming a mixture. The mixture is allowed toupwell within the up tube upward to a depth less than the predetermineddepth. The upwelling mixture is passed through a power generation unitto generate useful power.

In accordance with another embodiment the present invention provides asystem for generating power from differences in osmotic potentialbetween a source of relatively low salinity water and a source ofrelatively high salinity water. The system comprises an up tube locatedin the source of relatively high salinity water. The up tube is fluidlyconnected to the source of relatively high salinity water through one ormore openings in the up tube at a first depth. The up tube terminates ata depth in the source of relatively high salinity water at a seconddepth less than the first depth. A down tube is provided having a firstend connected to the source of relatively low salinity water and asecond end which discharges the low salinity water from the source ofrelatively low salinity water into the up tube such that the relativelylow salinity water and the relatively high salinity water form a mixturewhich upwells within the up tube. A means is provided for generatingpower from the rising mixture.

In accordance with another embodiment, the present invention provides asystem for generating power from differences in osmotic potentialbetween a source of relatively low salinity water and a source ofrelatively high salinity water. The system comprises a first tube forconducting a flow of relatively high salinity water from a first depthto a second depth, the first tube having a first cross-sectional area. Asecond tube is provided fluidly connected to the source of relativelylow salinity water at a first end and to the first tube at a second endat or near the first depth, where the second tube has a secondcross-sectional area. A third tube is provided for conducting a flow ofrelatively high salinity water from the second depth at or near a firstend of the third tube to the first tube at the second end, where therelatively low salinity water and the high salinity water form a mixturein the first tube. The mixture is caused to flow in the first tube,increasing the recoverable energy of the relatively high salinity waterin the third tube. A power generator is provided, disposed between thefirst and third tubes for generating power from the increase inrecoverable energy.

In accordance with another embodiment, the present invention provides amethod for generating power from the difference in osmotic potentialbetween a source of relatively low salinity water and a source ofrelatively high salinity water. A source of relatively low salinitywater is conducted through a first tube, where the first tube has afirst cross-sectional area. The relatively low salinity water isdirectly contacted with water from the source of relatively highsalinity in an enclosed second tube to form a mixture, where the secondtube has a second cross-sectional area. The second tube is in fluidcommunication with the source of relatively high salinity water throughone or more openings in a third tube. The contacting causes an increasein recoverable energy of the relatively low salinity water in the firsttube. The relatively high salinity water in the third tube is conductedthrough a power generation unit to generate mechanical and/or electricalpower.

For purposes of summarizing the invention and the advantages achievedover the prior art, certain objects and advantages of the invention havebeen described herein above. Of course, it is to be understood that notnecessarily all such objects or advantages may be achieved in accordancewith any particular embodiment of the invention. Thus, for example,those skilled in the art will recognize that the invention may beembodied or carried out in a manner that achieves or optimizes oneadvantage or group of advantages as taught herein without necessarilyachieving other objects or advantages as may be taught or suggestedherein.

All of these embodiments are intended to be within the scope of theinvention herein disclosed. These and other embodiments of the presentinvention will become readily apparent to those skilled in the art fromthe following detailed description of the preferred embodiments havingreference to the attached figures, the invention not being limited toany particular preferred embodiment(s) disclosed.

BRIEF DESCRIPTION OF THE DRAWINGS

Having thus summarized the general nature of the invention and itsessential features and advantages, certain preferred embodiments andmodifications thereof will become apparent to those skilled in the artfrom the detailed description herein having reference to the figuresthat follow, of which:

FIG. 1A is a schematic diagram representation of a conventional forwardosmosis process through a semi-permeable membrane;

FIG. 1B is a schematic diagram representation of a conventional reverseosmosis process through a semi-permeable membrane;

FIG. 2 is a schematic representation of an experimental up tubeupwelling apparatus for use in accordance with the present invention;

FIG. 3 is a graph of theoretical power recovery for different sizeddown-tubes and fresh water flow rates using the experimental upwellingdevice of FIG. 2;

FIG. 4 is a schematic representation of one embodiment of a hydrocraticgenerator having features and advantages in accordance with the presentinvention;

FIG. 5 is a schematic representation of an alternative embodiment of ahydrocratic generator having features and advantages in accordance withthe present invention;

FIG. 6 is a schematic representation of a further alternative embodimentof a hydrocratic generator having features and advantages in accordancewith the present invention;

FIG. 7A is a schematic representation of a further alternativeembodiment of a hydrocratic generator having features and advantages inaccordance with the present invention;

FIG. 7B is a side view of the up tube of FIG. 7A, showing the slots inthe side of the up tube;

FIG. 7C is a sectional view from below of the shaft support of FIG. 7A;

FIG. 7D is a sectional view from above of the vane drum of FIG. 7A;

FIG. 8A is a schematic representation of a further alternativeembodiment of a hydro-osmotic generator having features and advantagesin accordance with the present invention;

FIG. 8B is a side view of the up tube of FIG. 8A showing two sets ofslots in the side of the up tube;

FIG. 8C is a sectional view from below of the shaft support of FIG. 8A;

FIG. 8D is a sectional view from above of the vane drum of FIG. 8A;

FIG. 9A is a schematic view of an up tube with an open lower end with analternative embodiment of a down tube having a plurality of holes in thesides and the outlet end, having features and advantages in accordancewith the present invention;

FIG. 9B is a sectional view from below of the up tube and the outlet endof the down tube of FIG. 9A;

FIG. 10A is a schematic view of an up tube with an open lower end withan alternative embodiment of the down tube with a plurality of secondarydown tubes having holes in the sides and the outlet end, having featuresand advantages in accordance with the present invention;

FIG. 10B is a sectional view from below of the up tube and the outletend of the down tube of FIG. 10A showing the plurality of secondary downtubes and the holes on the outlet ends of the secondary down tubes;

FIG. 11 is a schematic view of an up tube with an open lower end with analternative embodiment of the down tube with a plurality of secondarydown tubes, having features and advantages in accordance with thepresent invention;

FIG. 12 is a schematic view of a down tube with a rotating hub and spokeoutlets with no up tube;

FIG. 13 is a schematic view of a down tube with a rotating hub and spokeoutlets with an up tube, having features and advantages in accordancewith the present invention;

FIG. 14 is a schematic view of a portion of an up tube comprising aplurality of concentric up tubes, having features and advantages inaccordance with the present invention;

FIG. 15 is a schematic representation of a modified up tube havingfeatures and advantages in accordance with the present invention;

FIG. 16 is a schematic illustration of a possible large-scale commercialembodiment of a hydro-osmotic generator having features and advantagesin accordance with the present invention;

FIG. 17 is a cutaway view of the turbine and generator assembly of thehydro-osmotic generator of FIG. 12;

FIG. 18 is a schematic view of an up tube with an open lower end, withan alternative embodiment of the rotating down tube, extendingsubstantially into the up tube, and having holes and turbines mountedthereon, having features and advantages in accordance with the presentinvention;

FIG. 19A is a schematic view of an up tube with a closed lower end, withan alternative embodiment of the rotating downtube, extendingsubstantially into the up tube, and having holes and turbines mountedthereon, having features and advantages in accordance with the presentinvention;

FIG. 19B is a side view of the up tube shown in FIG. 19A;

FIG. 20 is a schematic view of an up tube with an open lower end, withan alternative embodiment of the rotating downtube, extendingsubstantially into the up tube, and having holes and turbines mountedthereon, with rotating up tube and down tube, having features andadvantages in accordance with the present invention;

FIG. 21 is a schematic view of an up tube upwelling apparatus inaccordance with the present invention wherein a rotating helical screwis used to generate the power instead of a plurality of fan blades,having features and advantages in accordance with the present invention;

FIG. 22A is a side view of an alternative embodiment of a fan blade usedin accordance with the present invention; and

FIG. 22B is a schematic view showing the under portion of the fan bladeillustrated in FIG. 22A of the drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

As discussed in the Background section above, when solvent fluids havingdiffering osmotic potentials are contacted and mixed with each otherenergy is released. This released energy results from an increase inentropy of water (or other solvent) when it is transformed from its pure(fresh-water) state to its diluted (salt-water) state. Thus, an entropygradient is created whenever two bodies of water or other solventshaving differing solute concentrations are brought into contact with oneanother and begin to mix. This entropy gradient can be physicallyobserved and measured in the well-known phenomena known as osmosis.

Because the term “osmosis” is associated with a membrane, the term“hydrocrasis” is used as a term for the situation when solvent fluidshaving differing osmotic potentials are contacted and mixed with eachother in the absence of a membrane.

FIG. 1A schematically illustrates conventional forward osmosis through asemi-permeable membrane. Forward osmosis results in the flow of water 10(or other solvent) through a selectively permeable membrane 12 from alower concentration of solute 14 to a higher concentration of solute 14.Many references discuss osmotic potential or osmotic pressure in termsof pressure drop Π across a semi-permeable membrane since the easiestway to measure the effect is to measure the difference in height or feet(meters) of head between the high concentration side and the lowconcentration side of the membrane 12. Forward osmosis results in therelease of work energy.

FIG. 1B illustrates the condition of reverse osmosis whereby water (orother solvent) 10 under the influence of external pressure is forcedthrough a selectively permeable membrane 12 from a higher concentrationof solute 14 to a lower concentration of solute 14, thus squeezing outor extracting the pure solvent 10 from the solute 14. Reverse osmosis iswidely used in water purification and desalinization plants throughoutthe world. Reverse osmosis consumes work energy.

To illustrate the amount of work energy dissipated or released in theosmotic process consider a hypothetical example where a large containerof salt water is supported just under the surface of a large opencontainer of fresh water. Moreover, there is an osmotic membraneseparating the two containers of water. Attached to the vessel of saltwater and extending up out of the fresh water is a slender, tall tubewith a volume of exactly one cubic meter. This slender, tall tube isopen at the top, and this is the only opening to the salt water vessel.At the start of the hypothetical experiment the water level and pressurein both containers is identical and is at the bottom of the slender,tall tube. However, osmosis will cause the fresh water to flow into thecontainer of salt water through the membrane and raise the level of saltwater in the slender tall tube until the pressure exerted by the columnof salt water is sufficient to just cancel or oppose the osmoticpressure across the membrane.

Now, if the top of the tube is cut just below the highest level of watertherein, then salt water will begin spilling over and dropping from thetop of the tube as fresh water continues to flow through the membraneinto the salt water solution at an equal rate. Now, for each cubiccentimeter of fresh water that flows through the membrane, an equalvolume of salt water solution will be displaced from the top of the tubeand drop a certain distance. Clearly, work is being done through themechanism of osmosis, but how much work is being done? How much pressureis exerted by the column of salt water and what is the height of thecolumn?

For small concentrations of an ideal solution, van't Hoff's formula forosmotic pressure (Π) is:

Π=−CRT

where C=Molar Concentration, R=Gas Constant and T=Absolute temperature.For salt water there are two ions per molecule and:

wt(NaCl)=58.5 g

T=20° C.=293° K

R=8.3144 J/mole° K

C=35 ppt=35,000 g/m³

=(35,000×2/58.5 moles)/m³

=1200 moles/m³

Π=−(1200 moles/m³) (8.3144 J/mole° K) (293° K)

=−2.9'10⁶ N/m²

=−2.9×10⁶ Pa

=−29 atm.

Pascal's Law says:

p=ρgh

Setting p (pressure due to the height of a column of liquid) equal to Π(the osmotic pressure) and solving for the height of the column (h)gives:

ρ=1034 kg/m³

g=9.8 m/s²

h=(2.9×10⁶ N/m²)/((1034 kg/m³) (9.8 m/s²))

=290 m

The incremental work done to displace 1 kg of water is:

W=½ mgh

=(0.5)(1 kg)(9.8 m/s²) (290 m)

=1.4 kJ

Thus, the osmotic energy potential to be gained from remixing freshwater into saline ocean water is significant—about 1.4 kJ/kg of freshwater, or the equivalent of about 290 m-head of water for a conventionalhydropower system. If this source of stored energy could somehow beefficiently exploited, it could result in the production of enormousamounts of inexpensive electrical power from a heretofore untapped andcontinually renewable energy resource.

Let us now cut the tall tube just below the maximum height of the saltwater (290 meters) and attach a spigot. The salt solution wouldcontinuously flow out of the spigot. What force is generated when akilogram of water flows through the tube and falls back to the originalwater level?

W=Mgh

=(1 Kg)(9.8 m/s²) (290 m)

=2.8×10³ Joules

If the osmotic membrane had a sufficiently large surface area to allow aflow of one kilogram per second, then the system would be generating1.4×10³ Joules per second which is the same as 1.4 Kilowatts.

If a penstock was attached to the end of the spigot and that in turn wasattached to a hydroelectric generator placed at the original waterlevel, then that generator (at 100% efficiency) would deliver 1.4kilowatts of electrical power.

There actually would be no need for either the tall tube or thepenstock. The generator would not care if the head pressure wasgenerated by gravity or osmotic pressure. The same electricity would begenerated if the opening in the salt water vessel was directly connectedto the inlet of the generator.

This is, of course, not a practical system for generating electricitysince it relies on an infinitely large rigid vessel and an infinitelylarge osmotic membrane.

While many systems have been proposed for harnessing this osmotic energypotential, few if any have been commercially successful. One problem isthat most osmotic energy recovery systems rely on a conventional forwardosmosis process utilizing a semi-permeable membrane. Full-scalecommercial development and exploitation of such power-generation systemsis hampered by the large membrane surface area required to achieveadequate flow rates and the expense and difficulty of maintaining suchsemi-permeable membranes. Other systems require the use of exoticbio-elastic materials and/or the use of evaporators, condensers and/orheat exchangers to extract useful work energy from osmotic energypotential.

However, in the unrelated field of ocean mariculture it is known to usethe buoyancy effect of fresh water mixed with saline water to provideartificial ocean upwelling for purposes of enriching the waters in theupper photic zone of the ocean with nutrient rich waters from the loweraphotic zones. For example, U.S. Pat. No. 5,106,230, incorporated hereinby reference, describes a method for the controlled generation ofartificial oceanographic upwelling. The method includes introducing arelatively fresh-water input stream to a predetermined depth, where thefresh-water mixes with the nutrient-rich deep-sea water so as to form amixture. The mixture is lifted upward by a buoyancy effect brought aboutby its reduced density, whereby the mixture is conducted towards thesurface through an up pipe. The method results in upwelling of cold,nutrient rich water from the lower aphotic regions of the ocean to theupper photic regions where the nutrients may be beneficially used byaquatic sea life.

During recent prototype testing of a similar upwelling device it wasdiscovered, surprisingly, that the amount of upwelling flow achieved interms of kinetic energy of the overall mass flow was in excess of theinput energy into the system in terms of the buoyancy effect and kineticenergy resulting from the fresh water introduced into the up tube.Subsequent experiments using a modified upwelling device have confirmedthat the total hydraulic energy output of such system significantlyexceeds the total hydraulic energy input.

While an exact explanation for this observed phenomena is not fullyappreciated at this time, it is believed that the excess energy outputis somehow attributable to the release of osmotic energy potential uponremixing of the fresh water and the salt water in the up tube. Thisresult is particularly surprising since the modified upwelling deviceincorporated no semi-permeable membrane or other specialized systemcomponents heretofore thought necessary to recover such osmotic energypotential. Because no membrane is present, the term hydrocraticgenerator is applied to the apparatus. For completeness of disclosureand understanding of the invention, the experimental design used inmaking this discovery is described and discussed below:

Experimental Design

An experimental upwelling apparatus similar to that illustrated in FIG.2 was constructed using suitable corrosion resistant materials. Theocean was simulated by dissolving 1800 kilograms (2 tons) of sea salt ina 50,000 liter (15,000 gallon) swimming pool. The up tube 40 was a 15 cm(6 inch) inside diameter (i.d.) polyvinylchloride (PVC) tube 1.5 meterslong. In some experiments discussed herein, the top of the up tube 40was left open and unobstructed, as illustrated. In other experimentsdiscussed herein, a turbine was attached to the top of the up tube 40 toconvert kinetic flow energy into mechanical work energy. The down tube20 was a 1.8 cm (½ inch) i.d. (PVC) tube 1 meter long. Two 90° elbowsand a short piece of pipe were attached to the end of the down tube 20so that the fresh water was caused to exit upwards into the up tube 40from the down tube 20. The apparatus was attached to a float 48 by nylonsupport cables 50, and the outlet end 44 of the up tube 40 waspositioned about 15 cm below the surface of the salt water.

The down tube 20 was connected to a reservoir 25 of fresh water. Thereservoir 25 was kept at a constant level by continually filling withtap water and allowing the excess to flow out the spill-way 27 so thatthe flow rate of fresh water through the down tube 20 was keptessentially constant. According to measurements the water in thereservoir 25 contained about 300 ppm of dissolved solids at all times,and the salt water in the swimming pool contained between 34,000 and36,000 ppm of dissolved solids. The temperature of both the water in thereservoir 25 and the salt water was the same in any individualexperiment (18-20° C.), because the salt water tank was set into theground, and the fresh water in the reservoir came from buried pipes.

The experiment was started by filling the down tube 20 with water toeliminate air bubbles. The height of the reservoir was then adjusted toestablish a pressure head that determined the rate of flow of freshwater in the down tube 20. The reservoir 25 was then filled with freshwater which was then allowed to flow from the reservoir 25 through thedown tube 20 whereupon it was introduced into the lower portion of theup tube 40.

The experiment was monitored by periodically measuring the salinity atthe outlet end 44 of the up tube 40 using a Myron L., DS Meter (model512T5). The flow rate out of the outlet end 44 of the up tube 40 wascalculated by measuring the salinity at the outlet end 44 of the up tube40. In particular, FIG. 2 shows four reference points in theexperimental apparatus: Point 1 is the fresh water reservoir; Point 2 isat the outlet end 44 of the up tube 40 where the salinity was measured;Point 3 is immediately above the outlet end 24 of the down tube 20; andPoint 4 is inside the up tube 40 below the outlet end 24 of the downtube 20. The following salinities and densities were used in theanalysis of the data.

Salinity of Salt Water=35,000 ppm

Salinity of Fresh Water=300 ppm

Density of Salt Water=1.035

Flow rates were calculated using the following analysis. Since there wasa continuous tube from Point 1 to Point 3, the salinity and flow ratemust be the same at Points 1 and 3. Since the only inlets to the up tube40 are from Point 3 and Point 4, the flow at Point 2 must equal the sumof the flows at Point 3 and Point 4. The equation for the flow at Point4 is derived from the following analysis:

If:

Q_(i)=Flow at point i

=W_(T)/ρ per second

S_(i)=Salinity at point i

=(W_(S)/W_(T))

W_(S)=Weight of Salt in a Solution

W_(T)=Total Weight of Solution

ρ=Density of Solution

Then:

S₂=W_(S2)/W_(T2)

And since the flow past Point 2 comes from either Point 3 or Point 4:

S ₂=(W _(S3) +W _(S4))/(W _(T3) +W _(T4))

Substituting in:

W_(S)=S W_(T)

Results in:

S ₂=(S ₃ W _(T3) +S ₄ W _(T4))/(W _(T3) +W _(T4))

Substituting in:

W_(T)=Q ρ seconds

Results in:

S ₂=(S ₃ Q ₃ ρ ₃ +S ₄ Q ₄ ρ₄)/(Q ₃ ρ₃ +Q ₄ ρ₄)

Which gives an equation that has one unknown variable (Q₄).

Q ₄ =Q ₃(ρ₃/ρ₄) (S ₂ −S ₃)/(S ₄ −S ₂)

It can be assumed, within the accuracy of this experiment, that:

S₃=0

ρ₃=ρ₄

Which leaves:

Q ₄ =Q ₃ S ₂/(S ₄ −S ₂)

The following Examples 1-4 report the results of several experimentswhich were conducted using the experimental design described above andas illustrated in FIG. 2:

EXAMPLE 1

The apparatus shown in FIG. 2 was used to measure observed flow rates inthe up tube 40 with different fresh water flow rates introduced into thedown tube 20. Table 1 is a compilation of the results for flow rates atvarious points in the up tube 40 with two different flow rates of freshwater in the down tube 20. The flow rate at Point 1, the flow rate offresh water from the reservoir, and the salinity at Point 2 at theoutlet end 44 of the up tube 40 were measured parameters. The flow rateat Point 3, the outlet end 24 of the down tube 20, was the same as theflow rate at Point 1. The remaining flow rates were calculated using theequations discussed above.

TABLE 1 Flow Rates at Various Locations in the Up Tube Height ofSalinity Reservoir at Point Flow (10⁻⁴ m³/sec) (meters) 2 (ppt) Point 1Point 2 Point 3 Point 4 0.23 34 1.3 45.5 1.3 44.2 0.55 34 2.4 84.0 2.481.6

The results indicate that the flow rate of the mixedsalt-water/fresh-water solution at Point 2 at the outlet end 44 of theup tube 40 far exceeded the flow rate of fresh water at Point 1 andPoint 3. Introducing fresh water into the down tube 20 and allowing thesalt water to flow into the up tube 40 therefore generated higher flowrates at Point 2, at the top of the up tube 40.

In order to demonstrate that this higher flow rate at Point 4 was notdue to transfer of kinetic energy from the fresh water flow coming fromthe down tube 20, the following experiment was performed.

EXAMPLE 2

Flow Rates Through the Up Tube with Salt Water vs. Fresh WaterIntroduced Into the Down Tube

For this experiment, a 6″ turbine roof vent was attached to the outletend 44 of the up tube 40. One of the vanes was painted to allow for thecounting of rotations. The reservoir was filled with fresh water havinga salinity of 300 ppm in one experiment and with salt water having asalinity of 36,000 ppm in a second experiment. The reservoir was placedat a height of 0.55 meters above the water level of the salt water inthe pool. The fresh water was then allowed to flow through the down tube20, and the rate at which the turbine rotated was determined. Then, saltwater from the salt water pool was allowed to flow through the down tube20, and the rate at which the turbine rotated was again determined. Theresults are shown in Table 2 below.

TABLE 2 Turbine Speed with Fresh Water vs. Salt Water in Down Tube DownTube Water Flow Turbine Speed (10⁻⁴m³/sec) (rpm) Fresh Water (0.3 ppt)2.4 5.6 Salt Water (36 ppt) 2.3 2.3

As illustrated in Table 2, above, the turbine rotated 2.4 times morerapidly when fresh water was introduced into the down tube 20 than whensalt water was used. The higher turbine speed when fresh water wasintroduced into the down tube 20 is a direct indication that the waterflow in the up tube 40 was higher when fresh water rather than saltwater was introduced into the down tube 20 and that the higher observedwater flow rates from the top of the up tube 40 in Example 1 were notdue solely to kinetic energy transfer from the fresh water flow out ofthe down tube 20.

The kinetic energy transferred from the salt water in the down tube 20to the salt water in the up tube 40 would be at least as great (if notslightly greater due to increased density of salt water) as the kineticenergy transferred from the fresh water in the down tube 20. The resultsshown in Table 2 indicate that some, but not all, of the upwelling ofwater in the up tube 40 is due to kinetic energy transfer from the waterintroduced into the down tube 20.

The power which is available from the kinetic energy of the water flowat various locations in the up tube 40 can be calculated as follows:

P_(k)=Power from Kinetic Energy

=½ M_(q)v²

=½(η Q) (16Q²/Π²d⁴)

=8Q³ ρ/Π²d⁴

where:

A=Cross Sectional Area

=Πd/4

d=Tube Diameter

M_(q)=Mass Flow

=Q×ρ

ρ=1+(S_(i)/1000)

v=Velocity

=Q/A

Table 3 shows the calculated power attributable to kinetic energy at thethree points in the up tube 40.

TABLE 3 Kinetic Energy at Various Points in the Up Tube Salinity atHeight of Point 2 Kinetic Power (watts) Reservoir (meters) (ppt) Point 2Point 3 Point 4 0.23 34 0.16 0.02 0.14 0.55 34 0.98 0.11 0.90

In the following series of experiments, the diameter of the down tube 20and the rate of flow of the fresh water which was introduced into thedown tube 20 were varied to determine the dependence of the rate ofupwelling in the up tube 40 on these parameters.

EXAMPLE 3

A series of experiments were carried out using the experimental designdescribed above and as illustrated in FIG. 2, but with down tubes 20having different diameters. With each down tube 20, the flow rates ofthe fresh water in the down tube 20 were varied to determine the effectof different fresh water flow rates on available power. The salinity atthe outlet end 44 of the up tube 40 was measured, and the water flowrates were calculated from the salinity as before. The water flow rateswere used to calculate the available power at Point 2, the outlet end 44of the up tube 40. The available power was then normalized by dividingthe available power by the fresh water flow rate in the down tube 20.The results are shown in Table 4 below.

TABLE 4 Normalized Power Production vs. Diameter of Up Tube and FreshWater Flow Rates Ratio of Up Salinity Flow (× 0.0001 m³) Tube Area ofPower/Fresh at Point 2 Point Point Point Down Tube Down Tube Water Flow(ppt) 1 4 2 Area (m²) Area (Watts/m³) 31.8 22 259 281 0.000254 69.7 131232.6 18 309 327 0.000071 249 2715 33.4 5.2 158 163 0.000018 983 125631.4 33 334 367 0.000254 69.7 1877 32.6 26 446 472 0.000071 249 566433.3 7.6 211 218 0.000018 983 2047 35.0 5 168 173 0.000010 1770 1559

In all cases, the power per unit volume of fresh water introduced into adown tube 20 of a given diameter increased as the flow rate of freshwater through the down tube 20 increased. Thus, for the down tube 20with an area of 0.000254 m², the power/m³ of fresh water flow increasedfrom 1312 watts/m³ with a fresh water flow rate of 22×10⁻⁴ m³ to 1877watts/m³ with a fresh water flow rate of 33×10⁻⁴ m³. The same trend wasmaintained for the down tubes having areas of 0.000071 and 0.000018 m².Thus, the data illustrates that increasing the fresh water flow rate ina down tube 20 having a given area increased the normalized availablepower output of the device.

Second, although the power per unit volume of fresh water introducedinto the down tube 20 increased with increased volume of fresh waterintroduced into the down tube 20 in all cases, the percent increase inthe power with increase in fresh water flow rate was less for thelargest down tube 20 (0.000254 m² area) than for the other down tubes20. When the fresh water flow rate increased from 22×10⁻⁴ m³ to 33×10⁻⁴m³, or by 50%, with the largest down tube 20, the power/fresh water flowrate increased from 1312 watts/m³ to 1877 watts/m³, or 40%. Bycomparison, when the fresh water flow rate for the down tube 20 with anarea of 0.000018 m² was increased from 5.2 to 7.6×10⁻⁴ m³, or 46%, thepower/fresh water flow rate increased from 1256 watts/m³ to 2047watts/m³, or 62%, more than 1.5 times as much as for a comparablepercent change in the fresh water flow rate with the larger down tube20.

Similarly, when the fresh water flow rate for the down tube 20 with anarea of 0.000071 m³ increased from 18 to 26×10⁻⁴ m³, or 44%, thepower/fresh water flow rate increased from 2715 watts/m³ to 5664watts/m³ or 108%, more than 2.5 times as much as for the largest downtube 20. The efficiency of power production declined with the largestdiameter down tube 20.

These results are shown graphically in FIG. 3. The graphs depictedtherein appear to show that there is an optimum ratio (about 250:1) ofthe area of the up tube 40 relative to the area of the down tube 20 thatmaximizes normalized power production. At ratios higher or lower thanabout 250 the normalized power per unit volume of fresh water declines.

Although a ratio of the area of the up tube 40 relative to the area ofthe down tube 20 of approximately 250 appears to be optimal, the ratiomay range from approximately 5 to 50,000, more preferably from 50 to2000.

The previous examples and discussions illustrate that a suitablyconstructed upwelling apparatus as illustrated in FIG. 2 has thepotential of generating useful power by mixing aqueous liquids havingdifferent osmotic potentials. The simple experimental apparatusillustrated in FIG. 2 generates 0.98 watts with a fresh water flow of2.4×10⁻⁴ cubic meters per second. This is equivalent to 4 kilowatts percubic meter of fresh water per second, indicating an efficiency of about0.15%. The actual efficiency and capacity of a commercial-scale powerproduction facility will depend on a number of factors, including thesize of the up tube, the ratio of the flow area of the fresh water downtube 20 to the flow area of the up tube 40, and the rate of fresh waterflow. Those skilled in the art will recognize that the experimentalapparatus disclosed and discussed herein-above may be modified andimproved in other obvious ways to achieve even greater power productionand/or efficiency of operation.

The remaining detailed discussion and corresponding figures illustratevarious possible embodiments of a commercial hydrocratic generatorutilizing the principles discussed above and having features andadvantages in accordance with the present invention. Although thevarious embodiments of the apparatus depicted and described herein varysomewhat in design and operation, certain common features and advantageswill become readily apparent and, thus, the descriptions thereof willnot be repeated.

FIG. 4 is a simple schematic illustration of one possible embodiment ofa hydrocratic generator 100 utilizing the principles discussed above andhaving features and advantages in accordance with the present invention.The device 100 generally comprises a down tube 20, an up tube 40, and apower plant generator 60. The particular device illustrated in FIG. 4may be adapted for either large-scale deep water applications or forrelatively small-scale or intermediate-scale power generation facilitiesin shallow coastal waters, as desired. For example, the depth of waterillustrated in FIG. 4 may be 10 to 50 meters or more, with the up tube40 being 1-5 meters in diameter.

In a preferred embodiment, fresh water is introduced into the down tube20 in order to power the device. The term “fresh” water as used hereinis to be interpreted in a broad sense as water having an osmoticpotential relative to sea water. Thus, it may be used to describe theinput stream a river discharge, a mountain run-off, a treated sewagedischarge, a melting iceberg, or even runoff from a city storm drainagesystem.

The fresh-water input stream may be conducted though the down tube 20 byapplying pressure at the inlet end 22 of the down tube 20. The pressuremay be provided by a pumping station or with a hydrostatic head pressureresulting from a fluid reservoir at a higher elevation. The pressureapplied at the inlet end 22 of the down tube 20 need only be high enoughto overcome the hydrostatic head at the outlet end 24 of the down tube20.

It has been found that, when fresh water is introduced into the downtube 20, sea water flows into the up tube 40, causing upwelling in theup tube 40 that can be used to generate power with the power generator60. Some of this upwelling effect is due to the increased buoyancy ofthe mixed water in the up tube 20, because fresh water has a lowerdensity than sea water. However, far more upwelling of sea water isobserved than would be expected from this phenomenon alone. It isbelieved that the apparatus and the method is able to harness the energyavailable from the different osmotic potentials of fresh water and seawater. The amount of upwelling and the amount of power that is generatedin the device depend in part on the particular dimensions of the up tube40 and the down tube 20 and the flow rate of fresh water in the downtube 20.

As shown in FIG. 4, the down tube 20 has an inlet end 22 and an outletend 24. The inlet end 22 is connected to a supply 25 of relatively freshwater. For example, this fresh water supply 25 may comprise a reservoir,pump or other source as desired or expedient. The outlet end 24 of thedown tube 20 is open such that the fresh water discharges through theoutlet end 24 of the down tube 20 into the up tube 40. In alternativeembodiments the outlet end 24 of the down tube 20 may be connected to anintermediate mixing chamber (not shown) which then discharges into theup tube 40.

Although the down tube 20 may be any of a variety of diameters, onecriterion is to choose a diameter for the down tube 20 which minimizesthe resistance to fluid flow through the down tube 20. Resistance toflow through a tube decreases as the diameter of the tube increases.Choosing a large diameter for the down tube 20 therefore minimizes theresistance of the tube for a given flow rate.

Another criterion in choosing the diameter of the down tube 20 is tomaximize the amount and efficiency of power generated by the powergenerator 60. When the diameter of the down tube 20 exceeds a certainvalue relative to the up tube 40, it has been discovered that theefficiency of power generation declines as the diameter of the down tube20 is increased further. There is therefore an optimum in the ratio ofthe diameter of the down tube 20 relative to the diameter of the up tube40, and therefore the ratio of the area of the down tube 20 relative tothe area up tube 40, in order to maximize the efficiency of powergeneration. When the ratio of the area of the down tube 20 to the uptube 40 increases beyond the optimal value, the increase in efficiencyof power generation with increased fresh water flow in the down tube 20is less than with a down tube 20 having a smaller area relative to theup tube 40 area. Choosing the diameter of the down tube 20 to maximizepower production therefore involves tradeoffs to choose the maximumdiameter possible without losing power efficiency.

In the embodiment of the apparatus shown in FIG. 4, the outlet end 24 ofthe down tube 20 is located inside the up tube 40. In this embodiment,the outlet end 24 of the down tube 20 is preferably oriented so that theoutlet end 24 of the down tube 20 points upward.

The up tube 40 has an lower end 42 and an outlet end 44. In theembodiment of FIG. 4 both the lower end 42 and the outlet end 44 of theup tube 40 are open. In other embodiments, the lower end 42 of the uptube 40 may contain vanes or other means of directing water flow. Someof these alternative embodiments of the up tube 40 are illustrated inother figures herein.

Although the diameters of the lower end 42 and the outlet end 44 of theembodiment of the up tube 40 shown in FIG. 4 are equal, the lower end 42and the outlet end 44 of the up tube 40 may have different diameters inother embodiments. For example, the up tube may be positively ornegatively tapered to form a nozzle or diffuser. Alternatively, the uptube 40 can have a necked-down portion to form an accelerated flowthere-through.

In the embodiment of FIG. 4 the outlet end 44 of the up tube 40 isattached to a flotation system for locating the up tube 40 at apredetermined depth. Other means of locating the up tube 40 at apredetermined depth may also used in place of the flotation system, andthe invention is not limited to the embodiment shown in FIG. 4. Theflotation system shown in FIG. 4 comprises one or more floats 48 and oneor more support cables 50. The float 48 may be formed of Styrofoam, orit may comprise a plurality of individual air bags, drums, or any othersuitable material capable of producing buoyancy.

In some embodiments, the lower end 42 of the up tube 40 is attached tomooring cables 52. The mooring cables 52 extend from the lower end 42 ofthe up tube 40 to anchors 56 fixed on the sea floor. The mooring cables52 and the anchors 56 retain the up tube 40 in a predetermined locationon the sea floor. The lifting force of the float 48 transmitted throughsupport cables 50 retains the up tube 40 at a desired predeterminedvertical orientation.

In the embodiment shown in FIG. 4, the down tube 20 is also attached tomooring cables 52 which extend to anchors 56 on the ocean floor. Themooring cables 52 and anchors 56 hold the down tube 20 in place. Thedown tube 20 is arranged so that it discharges the fresh water into theup tube 40.

Just as choosing an optimal diameter for the down tube 20 involvestradeoffs, choosing the diameter of the up tube 40 also involvesoptimization. Increasing the diameter of the up tube 40 increases theamount of upwelling in the up tube 40 and therefore increases powerproduction. However, increasing the diameter of the up tube 40 increasesboth the size and the cost of the apparatus. Further, increasing thearea of the up tube 40 allows the use of a down tube 20 with a greaterarea without losing efficiency in generating power. The ratio of thearea of the down tube 20 to the area of the up tube 40 is therefore theparameter which is to be optimized rather than the diameter of eitherthe up tube 40 or the down tube 20 alone The optimal diameters for theup tube 40 and the down tube 20 are interdependent on one another,because the ratio of the areas of the two tubes is a more importantparameter in optimizing power production than the area, and thereforethe diameter, or either the up tube 40 or the down tube 20 alone.

Advantageously the down tube 20 and the up tube 40 are not subjected toexcessively high pressures. In the embodiment shown in FIG. 4, the uptube 40 contains the sea water entering from the lower end 42 of the uptube 40 and the fresh water coming out of the outlet end 24 of the downtube 20. Because the up tube 40 is operated at low pressures, the uptube 40 can be constructed of relatively inexpensive and lightweightmaterials such as plastic, PVC, lightweight concrete, and the like.

Although the down tube 20 is subjected to higher pressures than the uptube 40, the pressures in the down tube 20 are typically small. Thus,inexpensive materials can therefore generally be used for both the uptube 40 and the down tube 20. Suitable materials for constructing thedown tube 20 and the up tube 40 include, but are not limited to,polyvinyl chloride (PVC), fiberglass, polyethylene (PE), polypropylene(PP), concrete, gunite, and the like. Alternatively, other materialssuch as stainless steel or titanium may also be used. Because the uptube 20 and the down tube 40 are generally exposed to water ofrelatively high salinity, it is preferable to form the down tube 20 andthe up tube 40 from materials which are resistant to corrosion from saltwater. Although the materials listed above are, in general, resistant tocorrosion, some alloys of stainless steel are not suitable for extendeduse in salt water. If stainless steel is chosen as a material ofconstruction, it is preferable to select an alloy of stainless steelwhich is resistant to corrosion by salt water.

The outlet end 44 of the up tube 40 may extend to or above the surfaceof the sea or may be located at any depth beneath the surface of thesea. In one embodiment, the outlet end 44 of the up tube 40 is locatedin the photic zone so as to bring nutrient-rich deep-sea water to thephotic zone to enhance growth of the organisms in the photic zonethrough mariculture.

The length of the up tube 40 may vary, depending on a variety offactors. The length of the up tube is preferably sufficient to allowcomplete mixing of the fresh water with the salt water, but not so longas to cause unnecessary drag on the water flow. The optimal length willbe determined as that which allows maximum output flow rate and powerproduction for a given range of input fresh-water flow rates. The lengthof the up tube 40 may also be chosen based on a desire to facilitatemariculture, the promotion of growth of organisms in the sea by transferof nutrients from nutrient-rich depths to the nutrient-poor water atlesser depths. If mariculture is practiced, the lower end 42 of the uptube 40 is preferably located at a depth of the sea where largeconcentrations of nutrients are available, and the outlet end 44 of theup tube 40 is preferably located in the photic zone. In this embodiment,the up tube 40 carries nutrient-rich water from the depth of the lowerend 42 of the up tube 40 to the outlet end 44 of the up tube 40 in thephotic zone, where few nutrients are available, thereby enhancing growthof the organisms in the photic zone. The length of the down tube 20 isrelatively unimportant, provided that it is long enough to deliver thefresh water into the up tube.

The power generator 60 generates electricity from the water flow insidethe up tube 40. FIG. 4 shows one simplified form of a power generator 60suitable for use with the present invention. The power generator 60comprises one or more turbines or propellers 62 attached to a shaft 64.In a preferred embodiment, there are a plurality of propellers 62attached to the shaft 64. The shaft 64 is connected to an electricalgenerator 66. When water upwells in the up tube 40, the upwelling waterturns the propellers 62, which in turn rotate the shaft 64. The rotatingshaft 64 drives the electrical generator 66, thereby generating power.

Preferably, one or more shaft supports 68 are provided to support theshaft 64 to minimize wobbling of the shaft 64 while the upwelling waterturns the one or more propellers 62 attached to the shaft 64. In apreferred embodiment, a plurality of shaft supports 68 engage the shaft64 to support the shaft 64 to minimize wobbling. In the embodiment shownin FIG. 4, three shaft supports 68 are present to support the shaft 64,a lower shaft support 68, a middle shaft support 68, and an upper shaftsupport 68. Further details on the shaft supports 68 are given in FIG.7C, described later.

The propellers 62 on the shaft 64 may be inside the up tube 40, abovethe outlet end 44 of the up tube 40, or both inside the up tube 40 andabove the outlet end 44 of the up tube 40. The propellers 62 on theshaft 64 may be located above the middle shaft support 68, below themiddle shaft support 68, or both above and below the middle shaftsupport 68. In the embodiment of FIG. 4, the propellers 62 are locatedinside the up tube 40 below the middle shaft support 68. Similarly, theelectrical generator 66 may be conveniently located above or below thesurface of the water in which the up tube 40 is located. In theembodiment shown in FIG. 4, the electrical generator 66 is located abovethe surface of the water in order to minimize maintenance expense.

FIG. 5 shows an alternative embodiment of a power generator 60. In thiscase, the power generator 60 comprises propellers 62 attached to theshaft 64 both above and below the middle shaft support 68. The shaft 64is attached to the electrical generator 66, which generates electricalpower when the shaft 64 rotates due to the water flow in the up tube 40.Again, the electrical generator 66 of FIG. 5 is located above thesurface of the water. In alternative embodiments, the electricalgenerator 66 may be located below the surface of the water, if desired.

FIG. 6 shows a further alternative embodiment of a power generator 60 inwhich one or more spiral fans 70 are mounted on the shaft 64. Shaftsupports 68 may optionally be provided to minimize wobbling of the shaft64. The one or more spiral fans 70 may be attached to the shaft 64 abovethe middle shaft support 68, below the middle shaft support 68, or bothabove and below the middle shaft support 68. One or more spiral fans 70may be mounted on the shaft 64 on the outlet end 44 of the up tube 40.In an alternative embodiment, one or more spiral fans 70 may be mountedboth inside the up tube 40 and on the outlet end 44 of the up tube 40.In the embodiment of FIG. 6, the spiral fan 70 is attached to the outletend 44 of the up tube 40.

The spiral fan 70 comprises a plurality of spiral vanes 72. The waterflow up the up tube 40 contacts the plurality of spiral vanes 72,turning the one or more spiral fans 70 mounted on the shaft 64. Turningthe one or more spiral fans 70 rotates the shaft 64. The rotating shaft64 drives the electrical generator 66, generating electrical power.Again, the electrical generator 66 may be conveniently located above orbelow the surface of the water, as desired.

In the embodiment of the power generator 60 shown in FIG. 6, bothpropellers 62 and one spiral fan 70 are mounted on the shaft 64. Thepropellers 62 and spiral fans 70 may be mounted on the shaft 64 in anyorder, above, below, or both above and below the middle shaft support68. The propellers 62 and spiral fans 70 may also be mounted on theshaft 64 inside the up tube 40 and/or above the outlet end 44 of the uptube 40. In FIG. 6, propellers 62 are mounted on the shaft 64 inside theup tube 40 below the middle shaft support 68, and the single spiral fan70 is mounted on the outlet end 44 of the up tube 40. The electricalgenerator 66 is located above the water.

FIG. 7A shows a further alternative embodiment of the up tube 40 inwhich the lower end 42 of the up tube 40 is closed. The down tube 20passes through the closed lower end 42 of the up tube 40. Although FIG.7A shows that the down tube 20 is attached to one or more mooring cables52 which are attached to anchors 56 on the ocean floor, the down tube 20may also be supported by the closed lower end 42 of the up tube 40. Theclosed lower end 42 of the up tube 40 of FIG. 7A helps to keep the downtube 20 in position without the need for mooring cables 52 and anchors56.

The up tube 40 of the embodiment of FIG. 7A comprises a plurality ofslots 76, as shown in FIG. 7B. The plurality of slots 76 are open to thesurrounding sea and allow the sea water to enter the up tube 40. One ormore shaft supports 68 are attached to the up tube 40. One possibleembodiment of a suitable shaft support 68 is shown in FIG. 7C. The shaftsupport 68 comprises one or more hydrodynamic cross members 78 and abearing 80. The cross members 78 are attached to the up tube 40 at afirst end and to the bearing 80 at a second end, thereby suspending thebearing 80 inside the up tube 40. The bearing 80 can have a variety ofdesigns such as ball bearings, compression bearings, and the like. Thecross members 78 are preferably hydro-dynamically shaped so as to notslow down water flow in the up tube 40. The shaft support 68 supportsthe shaft 64, minimizing the wobbling of the shaft 64 when the shaft 64rotates.

The power generator 60 of the embodiment shown in FIG. 7A comprises avane drum 90 inside the up tube 40. The vane drum 90 comprises aplurality of rings 92 connected by a plurality of curved vanes 94. FIG.7D shows a sectional view of the vane drum 90. Each curved vane 94 isattached by a first edge 96 to each of the plurality of rings 92. Thecurved vanes 94 are attached to the plurality of rings 92 in a manner sothat the curved vanes 94 form a helical curve when viewed from the side,as shown in FIG. 7A. The helical curved shape of the curved vanes 94improve the efficiency of energy transfer from the water flow throughthe slots 76 on the up tube 40 compared to the efficiency of curvedvanes 94 which are not oriented with a helical curve. FIG. 7D shows thecurved vanes 94 attached to the ring 92 from above as illustrated inFIG. 7A. FIG. 7D also shows the preferred curved surface of the curvedvanes 94 as well as the helical orientation of the curved vanes 94 asviewed from above.

In one preferred embodiment, the vane drum 90 is attached to the shaft64. When the sea water is drawn into the up tube 40 through the slots76, the incoming water contacts the curved vanes 94, rotating the vanedrum 90, which in turn rotates the shaft 64. The rotating shaft 64 turnsthe electrical generator 66, generating power from the upwelling waterin the up tube 40.

FIG. 8A illustrates a further alternative embodiment of the powergenerator 60 comprising two vane drums 90, a first vane drum 90 belowthe middle shaft support 68 and a second vane drum 90 above the middleshaft support 68. In a preferred embodiment, both the first vane drum 90and the second vane drum 90 are attached to the shaft 64 so that theshaft 64 rotates when the vane drums 90 rotate due to the flow of waterthrough the slots 76 into the up tube 40. The rotating shaft 64 rotatesthe shaft of the electrical generator 66, generating electrical power.

In the embodiment of the up tube 40 shown in FIG. 8B, there arepreferably two sets of slots 76 in the up tube 40 and two vane drums 90.In another embodiment, there are two vane drums 90 as in the embodimentshown in FIG. 8A, but the up tube 40 comprises only a single set ofslots 76 in the up tube 40, as in the embodiment of the up tube 40 shownin FIG. 7B.

FIG. 9A shows an alternative embodiment of the down tube 20 in which aplurality of holes 110 are present in the side of the down tube 20. FIG.9B shows a view of the outlet end 24 of the down tube 20 of FIG. 9A. Theoutlet end 24 of the down tube 20 of FIG. 9A is sealed except for asingle hole 110. In alternative embodiments, a plurality of holes 110may be provided in the outlet end 24 of the down tube 20. The freshwater flowing through the down tube 20 of FIG. 9A flows out of theplurality of holes 110 and into the up tube 40. Although the embodimentof the apparatus shown in FIG. 9A shows the alternative down tube 20with the embodiment of the up tube 40 of FIGS. 4-6 with an open lowerend 42, the down tube 20 of FIG. 9A may also be used with the embodimentof the up tube 40 such as shown in FIGS. 7A or 8A with a closed lowerend 42.

FIGS. 10A and 10B show another embodiment of the down tube 20 in whichthe down tube 20 separates into a plurality of secondary down tubes 120In the embodiment shown in FIG. 10A, there are a plurality of holes 110in the secondary down tubes 120, similar to the embodiment of the downtube 20 shown in FIG. 9A. FIG. 10B shows a sectional view of the downtube 20 of the embodiment of FIG. 10A from below. In the embodimentshown in FIG. 10B the outlet end 24 of each of the five secondary downtubes 120 is closed except for a single hole 110. In the embodiment ofthe down tube 20 of FIGS. 10A and 10B, the fresh water that isintroduced into the down tube 20 exits the holes 110 to enter the uptube 40.

In other embodiments the down tube 20 may separate into a plurality ofsecondary down tubes 120, as in the embodiment of the down tube 20 ofFIG. 10A, but there are no holes 110 in the secondary down tubes 120,and the outlet ends 24 of the secondary down tubes 120 are open. In thisembodiment of the down tube 20 (not shown), the fresh water which isintroduced into the down tube 20 exits the open outlet ends 24 of thesecondary down tubes 120 to enter the up tube 40.

FIG. 11 shows an alternative embodiment of the down tube 20 in which thedown tube separates into a plurality of secondary down tubes 120. In theembodiment shown in FIG. 11, the down tube 20 separates into a pluralityof secondary down tubes 120 outside of the up tube 40. In the embodimentshown in FIG. 11, there are no holes in the secondary down tubes 120, asin the embodiments shown in FIGS. 9A and 10A. In other embodiments thereare a plurality of holes 110 in the secondary down tubes 120.

Although the embodiment of the apparatus shown in FIG. 11 shows thealternative down tube 20 with the embodiment of the up tube 40 of FIGS.4-6 with an open lower end 42, the alternative down tube 20 of FIG. 11may also be used with the embodiment of the up tube 40 such as shown inFIGS. 7A or 8A with a closed lower end 42.

FIG. 12 shows another embodiment of the down tube 20 in which the downtube 20 terminates in a hub 122. The hub 122 forms a cap on the downtube 20 and rotates freely on the down tube 20. A plurality of spokeoutlets 124 are fluidly connected to the hub 122. The plurality of spokeoutlets 124 emerge at approximately a right angle from the hub 124 andthen bend at a second angle before terminating in a spoke discharge 126.The spoke discharge 126 may have an open end or a partially closed endwhere the water from the down tube 20 discharges. The embodiment of thedown tube 20 shown in FIG. 12 is similar to a rotating lawn sprinkler.The hub 122 is attached to the shaft 64, which is in turn connected withthe electrical generator 66. In the embodiment shown in FIG. 12, thereis no up tube 40.

When fresh water flows through the down tube 20 and is discharged out ofthe spoke outlets 124, the hub 122, shaft 64, and electrical generator66 rotate, generating electrical power. In the embodiment shown in FIG.12, the energy generated by the electrical generator 66 comes almostexclusively from the kinetic energy from the water emerging from theplurality of spoke discharges 126, because there is no up tube 40 ormeans of generating power from hydrocratic energy generated from themixing of fresh water from the down tube 20 with water of high salinity.

FIG. 13 shows another embodiment of the down tube 20 similar to theembodiment of FIG. 12, with a hub 122, a plurality of spoke outlets 124,and a plurality of spoke discharges 126 at the ends of the spoke outlets124. The embodiment of FIG. 13 differs from the embodiment of FIG. 12 inthat the spoke discharges 126 discharge the fresh water from the downtube 20 into an up tube 40 with an open lower end 42 and a plurality ofpropellers 62 attached to the shaft 64. The fresh water which exits thespoke discharges 126 into the up tube 40 causes upwelling in the up tube40, rotating the propellers, which in turn drive the shaft 64. The shaft64 drives a electrical generator 66 (not shown), generating electricalpower.

In the embodiment of the apparatus shown in FIG. 13, the shaft 64 isrotated both by the discharge of water from the spoke discharges 126rotating the hub 122 and by the upwelling in the up tube 40 turning thepropellers 62, which in turn rotate the shaft 64. The energy generatedin the embodiment of the apparatus shown in FIG. 13 is therefore acombination of kinetic energy from the rotation of the hub 122, shaft64, and electrical generator (not shown) from the fresh water ejectedfrom the spoke discharges 126 and from hydrocratic energy generated fromthe upwelling in the up tube 40 from the mixing of fresh water from thespoke discharges 126 mixing with the water of high salinity entering theup tube 40 from the lower end 42.

FIG. 14 illustrates another embodiment of the up tube 40 in which thereare a plurality of nested up tubes 40 having increasing diameters. Thelower end 42 of each of the plurality of nested up tubes 40 is open.Fresh water is introduced into the down tube 20 causing upwelling in theplurality of up tubes 40 when the water of high salinity enters the openlower ends 42 of the nested up tubes 40.

Any of the embodiments of power generators 60 can be combined with theembodiment of the nested up tubes 40 of FIG. 14. For example, in oneembodiment, the propellers 62 of FIGS. 4 and 5 may be used as a powergenerator 60 in combination with the nested up tubes 40 of FIG. 14. Inanother embodiment, the power generator 60 may comprise one or morespiral fans 70, as shown in FIG. 6.

FIG. 15 shows another embodiment of the up tube 40 and power generator60. In the embodiment of FIG. 15, a plurality of turbines 130 aremounted on a shaft 64 inter-spaced between a plurality of stators 132.The stators 132 direct the water flow into the turbine blades of theturbines 130 to increase the efficiency thereof. The shaft 64 isconnected to an electrical generator 66 (not shown). When water upwellsin the up tube 40, the upwelling water turns the turbines 130, which inturn rotate the shaft 64 and the electrical generator 66, generatingpower.

In the embodiment shown in FIG. 15, the portion of the up tube 40surrounding the turbines 130 and stators 132 comprises a nozzle 134 andan expander 136. The nozzle 134 reduces the diameter of the up tube 40in the portion of the up tube 40 around the turbines 130 and stators 132from the diameter of the remainder of the up tube 40. By reducing thediameter of the up tube 40 with the nozzle 134 in the portion of the uptube 40 surrounding the turbines 130, the upwelling water is forced intoa smaller area and is accelerated to a higher velocity water flow thatcan be harnessed more efficiently by the turbines 130. Nozzles 134 andstators 132 can also be used with other embodiments of the powergenerator 60 illustrated herein.

FIG. 16 is a schematic illustration of a possible large-scale commercialembodiment of a hydrocratic generator having features and advantages ofthe present invention. While a particular scale is not illustrated,those skilled in the art will recognize that the device 200 isadvantageously suited for large-scale deep-water use 100-500 meters ormore beneath sea level. The up tube 240 extends upward and terminates atany convenient point beneath sea level. The diameter of the up tube maybe 3-20 meters or more, depending upon the desired capacity of thehydrocratic generator 200. This particular design is preferably adaptedto minimize environmental impact and, therefore, does not result inupwelling of nutrient rich water from the ocean depths.

Sea water is admitted into the device from an elevated inlet tube 215through a filter screen or grate 245. The filter removes sea life and/orother unwanted objects or debris that could otherwise adversely impactthe operation of generator 200 or result in injury to local sea lifepopulation. If desired, the inlet tube 215 may be insulated in order tominimize heat loss of the siphoned-off surface waters to colder water ator near full ocean depth. Advantageously, this ensures that thetemperature and, therefore, the density of the sea water drawn into thegenerator 200 is not too cold and dense to prevent or inhibit upwellingin the up tube 240.

The sea water is passed through a hydraulic turbine power plant 260 ofthe type used to generate hydraulic power at a typical hydro-electricfacility. The turbine and generator assembly is illustrated in moredetail in the cutaway view of FIG. 16. Water enters the turbine 261through a series of louvers 262, called wicket gates, which are arrangedin a ring around the turbine inlet. The amount of water entering theturbine 261 can be regulated by opening or closing the wicket gates 262as required. This allows the operators to keep the turbine turning at aconstant speed even under widely varying electrical loads and/orhydraulic flow rates. Maintaining precise speed is desirable since it isthe rate of rotation which determines the frequency of the electricityproduced.

As illustrated in FIG. 16, the turbine is coupled to an electricgenerator 266 by a long shaft 264. The generator 266 comprises a large,spinning “rotor” 267 and a stationary “stator” 268. The outer ring ofthe rotor 267 is made up of a series of copper wound iron cells or“poles” each of which acts as an electromagnet. The stator 268 issimilarly comprised of a series of vertically oriented copper coilsdisposed in the slots of an iron core. As the rotor 267 spins, itsmagnetic field induces a current in the stator's windings therebygenerating alternating current (AC) electricity.

Referring again to FIG. 16, the sea water is discharged from the turbineinto the up tube 240. Fresh water is introduced into the base of the uptube 240 by down tube 220. The mixing of fresh water into saline seawater releases the hydrocratic or osmotic energy potential of the freshwater in accordance with the principles discussed above, resulting in aconcomitant pressure drop (up to 190 meters of head) across thehydraulic turbine 260. This pressure drop in conjunction with theinduced water flow upwelling through the up tube 240 allows forgeneration of significant hydropower for commercial power productionapplications without adversely affecting surrounding marine culture.

With reference to FIG. 18 of the drawings, this embodiment shows an uptube 40 having an open lower end 42 and an open outlet end 44. A downtube 20 is provided which enters the up tube 40 through the lower end42, and extends to a point approximately midway along the length of theuptube, where it is sealed by a cap 302. A shaft 64 extends upwardlyfrom the cap 302, extending to a generator, not shown in FIG. 18, butsubstantially similar to generators shown in some of the Figuresdescribed above.

Although in the embodiment shown in FIG. 18, the down tube 20 is hown asextending to a point approximately midway up the length of the up tube40, this construction may, in practice, vary widely according to theconditions, length of the up tube 40, and other apparatus parameters.Thus, the down tube 20 may extend only a short distance into the up tube40, or it may extend well beyond the midpoint thereof, to a selectedheight.

The down tube 20 comprises an outside portion 304, located outside ofthe up tube 40, and an inside portion 306, located within the up tube40. The outside portion 304 and inside portion 306 of the down tube 20are connected to each other by a rotational connector 308, which, in theembodiment shown in FIG. 18 is at the level of the open lower end 42.However, this rotational connector 308 could be configured on the downtube 20 at any appropriate vertical position of the down tube 20.

The rotational connector 308 permits rotation of the inside portion 306relative to the outside portion 304, as will be described.

The inside portion 306 has a plurality of radial apertures 310, whichmay be randomly disposed on the inside portion 306, or specificallylocated, such as beneath a turbine 62, according to the selectedconfiguration of the generator. Fresh water entering the down tube 20from a supply source or reservoir passes through the rotationalconnector 308, and into the inside portion 306, where it must exitthrough one of the radial apertures. The cap 302 mounted at the top endof the inside portion 306 prevents any water or liquid from the downtube 20 from exiting the inside portion 306, except through the radialapertures 310.

The inside portion 306 and shaft 64 are secured appropriately inposition by shaft supports 68 to prevent wobbling or axial displacementthereof, as has already been described above in other embodiments.

In operation, fresh water exiting the down pipe 20 through the radialapertures 310 is mixed with water of higher salinity entering the lowerend 42 of the upper tube 40. The energy produced by the mixing of thewater of higher salinity and lower salinity drives turbine 62, which inturn rotates the inside portion 306, the cap 302, and the shaft 64. Thisembodiment permits accurate selection of apertures 310 for releasing ofthe fresh water into the up tube 40, in a manner that is fixed withrespect to the turbines 62. Since the radial apertures 310 and turbines62 are both rotating, the precise location of mixing, and the optimaleffect thereof of driving the turbine 62, can be exploited to improvethe efficiency and hence the energy produced by the apparatus of theinvention. This is achieved by the use of the rotational connector 308which allows relative rotation of the inside portion 306, but ensures noleakage or fresh water escape from the down tube 20 at the position ofthe rotational connector 308.

FIG. 19 shows a variation of the apparatus shown in FIG. 18, includingthe up tube 40, the down tube 20 having an outside portion 304, and aninside portion 306, the outside and inside portions 304 and 306respectively being connected by the rotational connector 308. A cap 302is provided at the top end of the inside portion 306, and a series ofturbines 62 are mounted on the inside portion 306, which has a pluralityof selectively placed radial apertures 310. The apparatus in FIG. 19differs from the embodiment shown in FIG. 18 by the existence of aclosure piece 320 over the lower end 42 of the up tube 40. Since theclosure piece 320 prevents sea water from entering the lower end 42 ofthe up tube 40, a plurality of holes 322 are provided at locations inthe wall of the up tube 40, as shown in FIG. 19B, through which the seawater is introduced to the interior of the up tube 40. One advantage ofthe embodiment shown in FIGS. 19A and 19B is that the sea water can beintroduced at the most efficient point, thereby facilitating control ofthe precise points or areas at which the sea water as well as the freshwater are first introduced and allowed to mix. This factor, coupled withthe orientation of turbines 62 on the inside portion 306, can be used tostreamline the efficiency of the apparatus. As was the case with respectto FIG. 18, the fresh water is only allowed to exit through the radialapertures between the rotational connector 308 and the cap 302, at aposition, flow-rate and orientation which can be controlled andmanipulated to advantage.

In FIG. 20 of the drawings, a further embodiment showing a variation ofthose illustrated in FIGS. 18 and 19 of the drawings is illustrated. Inthis embodiment, an up tube 40 is provided, as well as a down tube 20including an outside portion 304, an inside portion 306 having aplurality of radial apertures 310, and a cap 302. At the lower end 42, aclosure piece 320 is provided. In the embodiment shown in FIG. 20, therotational device 308 is positioned outside of the up tube 40 andclosure piece 320 so as to permit rotation of both the inside portion306 of the down tube 40, and the up tube 20, in response to energyproduction which causes rotation of the turbine 62. Thus, rotation aboutthe connector 308 as a result of forces on the turbines 62 therebyrotates the closure piece 320, up tube 40 and the inside portion 306 ofthe down tube 20.

As was the case in the embodiment shown in FIGS. 19A and 19B, sea waterwill enter the up tube 40, not through the lower end 42, but through aseries of holes 322 of the type shown in FIG. 19B. Alternatively,instead of having a plurality of holes 322, one or more slits may beprovided in the wall of the up tube 40, such as those shown in FIGS. 7Bor 8B of the drawings.

The embodiment of FIG. 20 is yet another variation by means of which theprecise location of entry of the fresh water and sea water respectivelyinto the up tube 40 can be controlled and exploited to derive maximumenergy and power following hydrocrasis and the energy released thereby.

FIG. 21 of the drawings shows a variation of the hydrocratic generatorof the invention which uses neither vanes nor turbines on the shaft 64,but rather a helical screw 330 mounted on the shaft, and which is causedto rotate in response to the energy released by mixing of the water withdifferent salinities. Such forces acting on the helical screw 330 rotatethe shaft 64, which in turn transmits rotational forces to the generatorfor use as described above.

FIG. 22A of the drawings shows an alternative embodiment for deliveringfresh water from the down tube 20 to a precise location with respect tothe fan blades. As shown in FIG. 22A, an inside portion 306 of the downtube 20 has a plurality of fan blades 62, also referred to as turbines,mounted thereon. Instead of exiting the inside portion 306 through aplurality of apertures, the fresh water in the inside portion 306 is fedthrough a fan tube 336 which is mounted on the underside 338 of the fanblade 62. Towards the outer extremity 340 of the fan blade 62, the fantube 336 includes a U-shaped section 342, terminating in an outlet 344.Thus, fresh water enters through the inside portion 306, flows along thefan tube 336, into the U-shaped section 342, and exits through outlet344. In the embodiment shown in FIGS. 22A and 22B, the fresh water thusflows from the interior pipe through a series of smaller pipes locatedunder the fan blades 62 (or helical screw, if this embodiment is used),to the outer edge of the fan blades 62. The direction of flow isreversed so the fresh water exits in a flow direction which is towardsthe center of the up tube 40.

The embodiment shown in FIGS. 22A and 22B allows the apparatus to takeadvantage, once more, of controlling the exit areas for the saline andfresh water, thereby pinpointing the reaction location for maximumenergy production and/or use of such energy in a manner which rotatesthe fan blades optimally. As with the other embodiments, the insideportion 306 of the down tube 20 is attached to a rotating shaft, whichin turn attaches to a generator or power mechanism which uses or storesthe energy so produced.

Other Applications/Embodiments

In the preferred embodiments discussed above, the up tube 40 is locatedin a body of water of high salinity and high negative osmotic potentialsuch as an ocean or a sea. The water of high salinity and high negativeosmotic potential enters the up tube 40 in a ratio of greater than 8:1salt water to fresh water, more preferably 30:1 salt water to freshwater, and most preferably about 34:1 or higher. The mixing of the freshwater of low negative osmotic potential with the sea water of highnegative osmotic potential in the up tube 40 causes upwelling and drawssea water into the up tube 40 through the openings. The upwelling waterin the up tube 40 rotates propellers 62, spiral fans 70 or turbines 130,261, which are attached to a drive shaft 64, 264. The rotating shaft 64,264 turns the electrical generator 66, 266 generating electrical powerfrom the difference in osmotic potential between the fresh waterintroduced into the down tube 20 and the water of high salinity whichenters the up tube 40 through the openings in the up tube 40.

Because the method depends on having solutions of different osmoticpotentials exiting the down tube 20 and entering the up tube 40, it ispreferable that the source of fresh water exiting the down tube 20 andthe source of the water of high salinity entering the up tube 40continue to have different osmotic potentials over time so that powergeneration continues over a long period of time. For example, if thebody of water of high salinity surrounding the up tube 40 is small, thefresh water exiting the down tube 20 can dilute the water of highsalinity after exiting the up tube 40, reducing the difference inosmotic potential between the fresh water and the water of highsalinity. Reducing the difference in osmotic potential between the freshwater exiting the down tube 20 and the water of high salinity enteringthe up tube 40 reduces the amount of energy available. It is thereforegenerally advantageous that the body of water of high salinity have alarge volume. Locating the up tube 40 in a large body of water havinghigh salinity such as the ocean or the Great Salt Lake is therefore apreferred embodiment.

Alternatively, the invention can be operated between bodies of saltwater having different salinity or between waters at different depths ofthe same body of water. For example, the salinity and temperature of seawater is known to vary with depth and location. In the Hawaiian islands,at a depth of 1000 meters, the ambient water temperature isapproximately 35° F., with a salinity of approximately 34.6 ppt. Thesurface temperature is approximately 80° F. with a salinity ofapproximately 35.5 ppt. Thus, an osmotic energy potential (albeit small)exists between the surface waters and the waters at 100 meters depth.

While the present invention is disclosed in the context of generatingpower by directly contacting and mixing fresh water with sea water in anapparatus located in the ocean, it is to be understood that theapparatus and method are not limited to this embodiment. The techniquesand concepts taught herein are also applicable to a variety of othersituations where aqueous solutions having differing osmotic potentialsare available. For example, in one embodiment, the apparatus and methodmay be applied to a concentrated brine from a desalinization plant beingmixed with the less-concentrated brine in sea water. In anotherembodiment, a treated sewage effluent, a fresh water stream, can bemixed with sea water. If desired, an osmotic membrane or osmotic waterexchange plenum may be provided at the outlet end of the down tubeand/or at the outlet (top) of the up tube in order to increase theefficiency of energy production. The apparatus and method may thus beapplied to a wide range of applications in which two solutions ofdiffering osmotic potential are available.

The various embodiments of the invention disclosed and described hereinare exemplary only. As such, these example embodiments are not intendedto be exhaustive of all possible ways of carrying out the invention oreven the most economical or cost-efficient ways of carrying out theinvention on a commercial scale. Many of the example embodimentsdisclosed and discussed herein are based on experimental testing ofsmall-scale models embodying certain features of the invention. Thesemodels and the test results reported herein may or may not be directlyrelevant to a full-scale power production facility utilizing theinvention. However, those skilled in the art will readily recognize fromthe examples disclosed and discussed herein the utility of the inventionin terms of its broader scope, and how it may be beneficially utilizedin a commercial power production facility to efficiently harness theosmotic energy potential between fresh water run-off and sea water (orother convenient bodies of water/solvent having different soluteconcentrations).

Thus, although this invention has been disclosed in the context ofcertain preferred embodiments and examples, it will be understood bythose skilled in the art that the present invention extends beyond thespecifically disclosed embodiments to other alternative embodimentsand/or uses of the invention and obvious modifications and equivalentsthereof. Accordingly, it is intended that the scope of the presentinvention herein disclosed should not be limited by the particulardisclosed embodiments described above, but should be determined only bya fair reading of the claims that follow.

What is claimed is:
 1. A method for generating power utilizing thedifference in osmotic potential between relatively low salinity waterand relatively high salinity water, the method comprising: conductingthe relatively low salinity water through a first tube having anon-rotatable portion and a rotatable portion, the rotatable portionhaving at least one aperture through which the low salinity water exitsthe first tube; directly contacting the relatively low salinity waterwith the relatively high salinity water in a second tube to form amixture, wherein the second tube is in fluid communication with therelatively high salinity water through one or more openings in thesecond tube, the contacting causing an increase in recoverable energy ofthe mixture in the second tube; and conducting the mixture through apower generation unit to generate mechanical and/or electrical power;and rotating the rotatable portion of the first tube using therecoverable energy of the mixture by selectively discharging therelatively low salinity water in a predetermined location relative tothe power generation unit.
 2. The method of claim 1, wherein the powergeneration unit comprises: a plurality of propellers, at least one ofthe propellers being mounted on the rotatable portion of the first tubesuch that the propellers, when rotating, rotate the rotatable portion ofthe first tube, the propellers being located inside the second tube; andan electrical generator coupled to the shaft for generating electricalpower.
 3. The method of claim 1, wherein the power generation unitcomprises: a vane drum comprising a plurality of vanes, at least one ofthe vanes being mounted on the rotatable portion of the first tube suchthat the vanes, when rotating, rotate the rotatable portion of the firsttube, wherein the plurality of vanes rotate a shaft when contacted withthe mixture; and an electrical generator connected to the shaft.
 4. Themethod of claim 1 wherein the power generation unit comprises: a helicalscrew at least a portion of which is mounted on the rotatable portion ofthe first tube such that the helical screw, when rotating, rotates therotatable portion of the first tube, wherein the helical screw furtherrotates a shaft when contacted with the mixture; and an electricalgenerator connected to the shaft.
 5. The method of claim 1, wherein thefirst tube has a first cross-sectional area which is 5 to 50,000 timessmaller than a second cross-sectional area of the second tube.
 6. Themethod of claim 5, wherein the first cross-sectional area is 50 to 2000times smaller than the second cross-sectional area.
 7. The method ofclaim 5, wherein the first cross-sectional area is approximately 250times smaller than the second cross-sectional area.
 8. The method ofclaim 1, wherein the mixture comprises the relatively high salinitywater and the relatively low salinity water in a ratio of at least 8:1.9. The method of claim 1, wherein the mixture comprises the relativelyhigh salinity water and the relatively low salinity water in a ratio ofat least 30:1.
 10. The method of claim 1, wherein the mixture comprisesthe relatively high salinity water and the relatively low salinity waterin a ratio of approximately 34:1.
 11. Apparatus for generating powerfrom differences in osmotic potential between relatively low salinitywater and relatively high salinity water, the apparatus comprising: anup tube for location in the relatively high salinity water, the up tubehaving one or more openings for admitting relatively high salinity waterthereto; a down tube having a non-rotatable section connectable to asource of the relatively low salinity water, a rotatable section whichdischarges the low salinity water into the up tube, and a rotationalconnecter member between the non-rotatable section and the rotatablesection so that the rotatable section can rotate relative to thenon-rotatable section, wherein the relatively low salinity water and therelatively high salinity water can form a mixture in the up tube whichcan rise in the up tube; and means for generating power from the risingmixture.
 12. The apparatus of claim 11 wherein the down tube has a firstcross-sectional area and the up tube has a second cross-sectional areaand the first cross-sectional area is 5 to 50,000 times smaller than thesecond cross-sectional area.
 13. The apparatus of claim 12 wherein thecross-sectional area of the down tube is 50 to 2000 times smaller thanthe cross-sectional area of the up tube.
 14. The apparatus of claim 11,wherein the power generation means comprises: a plurality of propellersat least one of which is located on the rotatable section such that thepropellers, when rotating, rotate the rotatable section of the downtube, the propellers being located inside the up tube; and an electricalgenerator coupled to the shaft for generating electrical power.
 15. Theapparatus of claim 11, wherein the power generation means comprises: avane drum comprising a plurality of vanes, at least one of the vanesbeing mounted on the rotatable section such that the vanes, whenrotating, rotate the rotatable section of the down tube, wherein theplurality of vanes rotate a shaft when contacted with the upwellingmixture; and an electrical generator connected to the shaft.
 16. Theapparatus of claim 11 wherein the power generation unit comprises: ahelical screw at least a portion of which is mounted on the rotatablesection of the down tube such that the helical screw, when rotating,rotates the rotatable section of the down tube, wherein the helicalscrew further rotates a shaft when contacted with the mixture; and anelectrical generator connected to the shaft.
 17. The apparatus asclaimed in claim 11 wherein the up tube has an open lower end whichcomprises the opening for admitting relatively high salinity water. 18.The apparatus as claimed in claim 11 wherein the up tube has a closuremember for closing a lower end thereof and a plurality of slottedopenings in a side wall thereof through which relatively high salinitywater is admitted.
 19. The apparatus as claimed in claim 18 wherein therotational connector member is further connected to the closure memberso that the up tube rotates with the rotatable section.
 20. Theapparatus as claimed in claim 11 wherein the rotational connector memberis further connected to the up tube so that at least a portion of the uptube rotates with the rotatable section.
 21. The apparatus as claimed inclaim 11 wherein the rotatable section comprises a plurality ofapertures therein for discharge of the relatively low salinity water.22. The apparatus as claimed in claim 11 wherein the rotatable sectionhas an end located in the up tube, the end having a cap thereon toprevent discharge of relatively low salinity water through the end. 23.The apparatus as claimed in claim 14 wherein at least one propellerlocated on the rotatable section comprises a hollow tube having a firstend in fluid communication with the rotatable section and a second enddisposed remotely from the rotatable section, the second end having anoutlet for discharging relatively low salinity water from the hollowtube.